Gas regulation system for blast furnace

ABSTRACT

A system for introducing a homogenous mixture of natural gas and oxygen into the tuyeres of a blast furnace. Included in this system are gas conduits with flow controllers connected to a mixer that produces a homogenous mixture. Provisions are made to by-pass the mixer and to introduce inert gas into the mixer to prevent formation of explosive gas mixtures.

BACKGROUND OF THE INVENTION

This invention relates to the field of ferrous metallurgy, specificallythe blast-furnace process, and is applicable to feeding natural gas intoblast furnaces.

In trying to reduce fuel consumption in a blast-furnace process byburning natural gas in a more efficient way, various gas regulationsystems for blast furnaces have been developed.

One system was designed for regulation of the pressure and rate ofnatural gas injected into a blast furnace and for its distribution amongthe air tuyeres. That system consisted of: a natural gas supplypipe-line provided with a shutoff, safety, measuring and controlinstruments, a bypass line complete with gate valves and gas vent, and acircular manifold with connections for feeding gas to each air tuyere,the circular manifold provided with shutoff and safety devices. This gasregulation system suffers from a number of drawbacks. Among them are;lack of measuring and regulating devices in connecting pipes feedingnatural gas to tuyeres, lack of devices preventing the formation ofexplosive mixtures in the gas regulation system, lack of a system formaintaining the prescribed ratio between the natural gas and blast air(or blast oxygen) flow rates, and lack of devices for preparation ofnatural gas for efficient combustion in the tuyere zone.

Another gas regulation system for use with a blast furnace, is the oneconsisting of the natural gas pipe-line with shutoff, safety, measuringand control instruments, a pipe-line, connected to the natural gas lineand equipped with shutoff and control instruments, for purging andfilling it with inert gas; a bypass line with shutoff and regulationinstruments, and a distributing manifold with connections, equipped withshutoff, safety, measuring and regulating instruments, for feeding thegas to each air tuyere. This gas regulation system eliminates most ofthe drawbacks of the previous system but retains its main weakness,namely inability to prepare natural gas for efficient burning in a blastfurnace which leads to excessive fuel usage in making pig iron.

BRIEF SUMMARY OF THE INVENTION

The goal of the invention is to improve the last described process aboveto reduce the rate of fuel usage rate in the blast-furnace process.

In order to achieve this goal the present invention includes a gasregulation S system for a blast furnace consisting of natural gas andinert gas pipe-lines, a distributing manifold with gas supply lines toair tuyeres and a bypass pipe-line, as well as shutoff, safety,measuring and control instruments installed in those pipe-lines and amixer in the natural gas pipe-line and an oxygen supply pipe connectedto the mixer, with a by-pass pipe connected to the natural gas pipe-linebefore and after the mixer, and an inert gas pipe-line connected to theoxygen supply line.

Thus in one aspect the present invention is a system for introducing amixture of natural gas and oxygen into the tuyeres of a blast furnacehaving a source of natural gas connected to a mixer via a natural gassupply pipe or conduit, the pipe having, upstream of the mixer, a flowcontrol valve to initiate, control and terminate flow of a natural gasto the mixer, flow control means between the flow control valve and themixer, with a check valve between the flow control means and the mixer,a source of oxygen connected to the mixer via an oxygen supply pipe orconduit the pipe having, upstream of the mixer a flow control valve toinitiate, control and terminate flow of oxygen to the mixer, flowcontrol means followed by a check valve between the flow control valveand the mixer, means to introduce an inert gas into the mixer, and meansto by-pass the mixer to deliver natural gas, without mixing with oxygenand/or inert gas, directly to the blast furnace tuyeres.

In a preferred embodiment of the invention the mixer is made in the formof a cylindrical chamber with a diameter to length ratio being in therange of 0.4-0.7. A perforated tube, connected to the oxygen supplypipe-line with one end closed, is inserted into the cylindrical chamberwith the longitudinal axis of the tube perpendicular to the longitudinalaxis of the cylinder, wherein diameter of the perforated tube is equalto 0.15-0.5× the diameter of the cylindrical chamber of the mixer. Thetotal area of the holes in the perforated tube is in the range of0.3-0.6× the flow area of the tube with the diameter of holes in therange of 0.03-0.07× the tube diameter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic representation of a gas regulation systemaccording to the present invention.

FIG. 2 is a schematic representation of a mixer according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1 the gas regulation system includes: a natural gaspipe line or conduit 10 connected to a source of natural gas 12, anoxygen pipe-line or conduit 14 connected to a source of oxygen 16 andinert gas pipe-line or conduit 18 connected to a source of inert gas 20,a bypass line or conduit 22, a manifold 24 with delivery pipe-lines orconduits 26 for supplying the gas to blast furnace (air) tuyeres 28, anda mixer 30.

Pipe-lines 10, 14, and 18 are designed to feed natural gas, oxygen andinert gas, e.g. nitrogen, respectively into the mixer 30. The bypasspipe-line 22 serves to supply natural gas directly into the manifold 24bypassing the mixer 30. Manifold 24 and delivery pipe-lines 26 areintended to supply natural gas or a natural gas/oxygen mixture to theblast furnace tuyeres 28. The mixer 30 is designed to obtain ahomogeneous mixture of natural gas and oxygen.

Natural gas pipe-line, conduit or supply line 10 is equipped with ashut-off or control valve 32 to initiate or terminate the flow ofnatural gas from source 12, a bleeder control valve 34 leading to ableeder valve or device 36 to vent natural gas or purge the system, anorifice plate 38, solenoid operated valve 40, regulating valve 42, checkvalve 44, mixer 30 and mixer isolation valves 46 and 48 together withmixer bypass conduit 22 and mixer by-pass valve 50. Pipe-line 10supplies natural gas to a manifold 24 which supplies pipe-lines (e.g.26) which in turn supply the natural gas to the blast furnace tuyere(s)28. Delivery pipe-line or conduit 26 includes natural gas flow controlvalve 52, flow plate 54 and flow plate isolation valves 56 and 58 and acheck valve 60. Manifold 24 also includes a vent or recovery conduit 62with a manual control valve 64 and solenoid operated control valve 66leading to a bleeder valve or recovery or vent system 68.

Oxygen pipe-line, conduit or supply line 14 is equipped with a manualcontrol valve 70, a dust collector or separator 72 with a clean outvalve 74. Dust collector 72 serves to remove solid particulate materialfrom the oxygen. The pipe-line 14 is fitted with a bleeder control valve76 leading to a bleeder valve, recovery or vent system 78. Downstream ofthe system 78 is an orifice plate 80, regulating valve 82, solenoidoperated control valve 84 and a shut-off valve 86 upstream of thelocation 88 where the nitrogen pipe-line 18 enters a common conduit 90which is connected through a check valve 92 and control valve 94 to themixer 30 as will hereinafter be more fully explained.

Nitrogen pipe-line, conduit or supply line 18 includes a cut-off valve96 to initiate or terminate nitrogen flow through conduit 18, controlvalve 98 and check valve 100 leading to a surge tank 102. Inclusion ofsurge tank 102 is intended to enable the user to create an emergencyreserve by accumulation of an excess amount of inert gas. Surge tank 102can be bled or vented through a system including a control valve 104leading to a recovery or vent 106. Downstream of surge tank 102pipe-line 18 includes an orifice plate 108 a shut-off valve 110 a branchline or conduit 112 with a control valve 114 leading to a bleeder, ventor recovery system 116, a control valve 120 upstream of a check valve122, in pipe-line 18 prior to its entry into the common conduit 90 atlocation 88.

Shut off devices, which include gate valves, solenoid-operated andmanually operated valves, as well as regulating valves and cutoffvalves, serve to shut off, or isolate from the gas regulation system,separate pipe-lines or sections of pipe-lines when gases supplied to thesystem are stopped, i.e., during repair and maintenance work and inemergency situations.

Safety devices which include check valves and bleeder valves areintended to a) automatically cut off oxygen supply to the mixer, b) toautomatically switch on and continuously feed inert gas into the oxygenpipe-line and, c) cut off inert gas automatically with reduction of itspressure in the outer circuit in emergency situations, as well as, d) tobleed a certain amount of oxygen and inert gas from the system in caseof excessive pressure.

Measuring instruments in addition to the orifice plates or flow meterscan include pressure and temperature sensors, to measure; the flow ratesof natural gas, oxygen, inert gas, natural gas/oxygen mixtures and blastair, the pressure of natural gas, oxygen, inert gas and blast air, and,the temperature of the natural gas/oxygen mixture. Instruments, notshown in FIG. 1, are intended to regulate oxygen pressure, natural gaspressure and flow rates of natural gas, oxygen and natural gas/oxygenmixtures. Such instrumentation is well known in the art.

Referring to FIG. 2 during the operation of the gas regulation systemnatural gas and oxygen are supplied into the mixer 30 through pipe-lines10 and 14 at the pre-assigned pressure values and preset ratio of flowrates. A homogeneous natural gas/oxygen mixture formed in the mixerarrives at the manifold 24 and via connecting pipe-lines 26 is fed intotuyere(s) 28. The mixer 30 includes a cylindrical chamber portion 130which is disposed in pipe-line or conduit 10 between valves 46 and 48with the axis of rotation of the cylinder coincident with or parallel tothe longitudinal axis of pipe-line 10. A tube 132 communicating with thecommon pipe-line 90 downstream of valve 94 is placed into thecylindrical portion 130 of mixer 30 generally perpendicular to the axisof rotation of the cylindrical chamber portion 130. The tube 132 has aclosed end 134 and a plurality of perforations 136. The tube 132 isfixed in fluid tight relation to the cylindrical chamber portion 130with all of the perforations 136 inside of the chamber 130.

Inert gas (e.g. nitrogen) via pipe-line (18) is mixed with or injectedinto the oxygen from pipe-line (14) in common conduit 90 during thestart-up of the gas regulation system in order to prevent the formationof explosive mixtures.

The maximum homogeneity of the natural gas/oxygen mixture is provided atthe following ratios;

diameter of the mixer cylindrical chamber to its length 0.4-0.7

diameter of perforated tube to diameter of cylindrical chamber 0.15-0.5

diameter of holes in perforated tube to its diameter 0.03-0.07

total area of holes in the tube to its flow section 0.3-0.6

which ratios were determined experimentals.

A system according to the invention was fabricated and installed in ablast furnace shop in Cherepovets in the Russian Federation. The systemhad a mixer fabricated as shown in FIG. 2 with the following dimensions:

A. Cylindrical Chamber Portion (130)

Inside Diameter 410 mm (16.14 inches)

Length 750 mm (29.52 inches)

B. Tubes or Perforated Pipe (132)

Inside Diameter 100 mm (3.93 inches)

Total Cross-sectional Area of Holes or Perforations 3532 mm² (5.48 sq.inches)

Number of holes or perforation 180

Diameter of each hole or perforation 5 mm (0.20 inches)

The mixing chamber was operated to provide a homogeneous mixture of 20%oxygen, balance natural gas when the oxygen flow to the perforated pipewas 52 Nm³ (1940.6 std ft³)/minute and natural gas flow was 208 Nm³(7762.6 std ft³)/minute.

When natural gas arrives at the tuyeres in the form of a uniform mixturewith oxygen, the process of burning of natural gas accelerates whichprovides for its complete combustion in the tuyere zone, increases cokereplacement ratio and decreases coke and total fuel consumption duringblast furnace operation.

Having thus illustrated and described the invention herein withreference to certain specific embodiments, the present invention isnevertheless not intended to be limited to the details shown.Furthermore, various modifications may be made in the details within thescope of the invention that is defmed in the appended claims.

What is claimed is:
 1. A gas mixing apparatus for introducing a mixtureof natural gas and oxygen into tuyeres of a blast furnace comprising incombination: a source of natural gas connected to a mixer, via a naturalgas s supply pipe or conduit, said pipe having, upstream of said mixer,a flow control valve to initiate, and terminate flow of natural gas tosaid mixer, flow control means between said flow control valve and saidmixer, with a check valve between said flow control means and said mixerto control flow of said natural gas to said mixer; a source of oxygenconnected to said mixer via an oxygen supply pipe or conduit, said pipehaving, upstream of said mixer, a flow control valve to initiate, andterminate flow of oxygen to said mixer, flow control means followed by acheck valve between said flow control valve and said mixer to controlflow of oxygen to said mixer; means to introduce an inert gas into saidmixer; and means to by-pass said mixer to deliver natural gas withoutmixing with oxygen and/or inert gas directly to said blast furnacetuyeres.
 2. A gas mixing apparatus according to claim 1, wherein a dustcollector means is included in said oxygen supply pipe between said flowcontrol valve and said flow control means.
 3. A gas mixing apparatusaccording to claim 1, wherein said means to introduce inert gas intosaid mixer includes a source of inert gas connected to an inert gas pipeor supply conduit, a flow control valve to initiate or terminate inertgas flow in said inert gas pipe, a surge tank between said flow controlvalve and a common pipe or conduit leading to said mixer connected tosaid oxygen and inert gas pipes upstream of said mixer, and flow controlmeans between said surge tank and said common pipe with a check valvebetween said flow control and said common pipe.
 4. A gas mixingapparatus according to claim 1, wherein said mixer is a cylindricalchamber connected to said natural gas supply pipe downstream of saidcheck valve, with a tube having a first or supply end connected to saidoxygen supply conduit downstream of said check valve, and a second orclosed end with said tube having a plurality of perforations through aportion of its length, said perforations proximate said closed end ofsaid tube, said tube inserted into said cylindrical chamber with theaxis of rotation of said tube disposed perpendicular to the axis ofrotation of said cylinder, and said tube in fluid tight communicationwith said cylindrical chamber, said perforations in said tube beingentirely within said cylindrical chamber.
 5. A gas mixing apparatusaccording to claim 4, wherein the diameter to length ratio of thecylindrical chamber is equal to 0.4-0.7.
 6. A gas mixing apparatusaccording to claim 4, wherein diameter of the perforated tube is equalto 0.15 to 0.5× the diameter of cylindrical chamber of the mixer.
 7. Agas mixing apparatus according to claim 4, wherein the total area ofperforations in the perforated tube is in the range of 0.3 to 0.6× thetotal flow area of the tube.
 8. A gas mixing apparatus according toclaim 4, wherein the diameter of each hole in the perforated tube is inthe range of 0.03 and 0.07× the diameter of the tube.
 9. A gas mixingapparatus according to claim 1 including means to purge said natural gasconduit upstream of said flow control means.
 10. A gas mixing apparatusaccording to claim 4 including means to purge said oxygen conduitbetween a dust collector placed downstream of said flow control valveand said flow control means.
 11. A gas mixing apparatus to claim 1,wherein said means to introduce an inert gas into said oxygen supplyconduit includes a source of inert gas connected to said oxygen supplyconduit via an inert gas pipe or conduit, said pipe having upstream ofsaid oxygen supply conduit a flow control valve to initiate, control andterminate flow of inert gas to said oxygen supply conduit, a surge tankdownstream of said control valve between a first check valve and a flowcontrol means, a second control valve between said flow control and saidoxygen conduit, and a second check valve between said second controlvalve and said oxygen conduit.
 12. A gas mixing apparatus according toclaim 9 including a first means to purge said surge tank and a secondmeans to purge said inert gas conduit between said second control valveand said second check valve.